Tanning



Patented Aug. 16, 1938 UNITED STATES 2.127.304 TANNING Gustav Mauthe andHermann Noerr, Leverkusen-- I. G. Werk, Germany,

asslgnors to I. G. Farbenindustrie Aktiengesellschatt,Frankfort-onthe-Main, Germany No Drawing. Application November'l, 1936,Se-

rial N0. 109,679.

Germany November 9,

6 Claims. (01.140-) The present invention relates to a process for themanufacture of leather.

More especially our invention is concerned with a modification andimprovement of the method 5 of tanning animal hides and skins with theaid of watersoluble zirconium compounds. It is known that by treatinghides and skins with watersoluble zirconium salts well tanned leathersof a light white color can be obtained. However,

as regards the shade and uniformity of their coloration they still showsome disadvantages in so far as the shade of the finished leatherdepends very much on the color of the original hide; for instance, adark or patchy-colored hide will not yield a leather of the desireduniform white color. Besides, uniform deacidification and alsouniform'taking-up of fat in the so-called liquor-process meet withcertain diificulties, the feel and shade of the finished leather beingoften somewhat impaired during the said stages of manufacture.

We have now found that the aforementioned disadvantages can be greatlydiminished by applying to the hides or leathers in any desired stage ofthe tannage an aqueous solution of a watersoluble silicic acid compound.As such compound, for example, watersoluble colloidal silicic acid orwatersoluble silicates, like the alkali silicates, may be applied to thehides or leathers at different stages of the tannage; for instance, theymay be added to the tanning liquors or to any of the finishing bathsused in the manufacture of leathers.

A particularly advantageous method in accordancce with our inventioncomprises neutralizing the acid zirconium salt tanning liquor during thelast phases of the tannage by gradually adding a silicate solutionthereto, or on the other hand, deacidifying the leathers in a fresh bathby means 0 of a silicate solution. It is well worth noticing that in ourprocess we may use an amount of silicates which per se would be quiteinsufflcient to effect any tanning of the silicate tannage type alsoknown in the art. I The leathers obtained. according to our saidinvention besides being unimpaired as regards their touch, feel andother properties, exhibit a pure white and uniform color, even if theoriginal hides were dark or unevenly colored.

The following examples illustrate the invention without limiting itthereto, the percentages being calculated on the weight of the hides.

Example 1 100 kgs. pickled calf hides are tannedin a solution of 8%anhydrous sodium sulfate in 100% of water, to which gradually during thetannage a solution of 7.8% of zirconiumoxychloride and I hydrochloricacid (basicity of the solution: 25%) has been added. After neutralizingwith an aqueous solution of sodiumbicarbonate the material is pared anddrummed in 400% of water at 30 C. During drumming, a dilute solution of4% of water glass (technical, 39 B.) is gradually added in severalportions, and the whole is caused to drum for a further half hour.Thereupon the leathers are rinsed in running water, until the leathercut shows a pI-I-value of 4.5 to 4.8, and afterwards greased. Taking upof fat takes place much more slowly and evenly than with thenonaftertreated leather, and the feel is less greasy.

After slicking, drying, moistening, staking, tacking and drying, thefinished leather exhibits a uniform pure white shade.

Example 2 Cow hides having received a formic acid pickle are treated ina solution of 60% water, 2% common salt and 4% sodium sulfate, to whicha solution of 20% water, 7% zirconiumoxychloride and 0.8% sulfuric acid(66 B.) is added in 4 parts in intervals of half an hour. After about 6to 8 hours an aqueous solution of 3% water glass of 37 B. diluted 1:10with water, is gradually added to the tanning liquor during one hour andthe hides are treated therein for another hour. Thereafter the leatheris staked for 24 hours, trimmed, rinsed until it shows a pH of 4.5 andfat-liquored. For the water glass an equivalent amount of potassiumsilicate may be substituted with a similar'result.

We claim:-

1. In the process of tanning with watersoluble zirconium compounds themodification which comprises applying to the hide or skin material inany stage of the tannage an aqueous solution of a watersoluble silicicacid compound of the group consisting of water soluble colloidal silicicacid and the water soluble silicates.

2. In the process of tanning with watersoluble zirconium compounds themodification which comprises gradually adding during the last phases ofthe tannage an aqueous solution of a watersoluble silicic acid compoundof the group consisting of water soluble colloidal silicic acid and thewater soluble silicates to the tanning liquor.

3. In the process according to claim 1 a modification in which awatersoluble alkali silicate is used as the watersoluble silicic acidcompound.

4. In the process according to claim 2 a modification in which awatersoluble alkali silicate is used as the watersoluble silicic acidcompound.

5. In the process according to claim 1 a modification in which waterglass is used asthe watersoluble silicic acid compound.

6. In the process according to claim 2 a modification in which waterglass is used as the'watersoluble silicic acid compound.

GUSTAV MAUTHE. HERMANN NOERR. Q

